Pulverulent metallic substance for electromagnetic purposes



Patented June 13, 1944 PULVERULENT METALLIC SUBSTANCE FORELECTROMAGNETIC PURPOSES Georg Trageser, Ludwigshafen-on-the-Rhine,Germany, assignor, by mesne assignments, to General Aniline & FilmCorporation, New York, N. Y-., a corporation of Delaware No Drawing.Application October 23, 1939, Serial No. 300,807. In Germany October 22,1938 (Granted under the provisions of sec. 14, act of March 2, 1927; 3570. G.

4 Claims.

The present invention relates to a process of improving the electric andmagnetic properties of pulverulent metals and alloys, especially ofnickel and iron and nickel-iron alloys.

According to the process .of U. S.- Patent No. 2,041,493, pulverulentalloys, in particular nickeliron alloys, are obtained in an especiallyadvantageous manner by thermally decomposing a mixture of the carbonylsof the desired alloy constituents, coating the particles of theresulting metal powder with a substance hindering the fritting togetherthereof and then heating the coated powder in a non-oxidizing, i. e. aninert or reducing atmosphere so that alloy formation takes place bydiflusion within the particles of the metal powder without smelting.

I have now found that pulverulent metallic substances with valuableelectric and magnetic properties can be obtained by coating the metallicpowder particles with inorganic halides which are practically notvolatile at high temperatures, heating the coated powder in anon-oxidizing atmosphere and removing the said halides from the heatedparticles to a far-reaching degree. Especially pulverulent alloys whichare obtained by thermal decomposition of mixtures of metal carbonyls,such as nickel-iron powder, can be materially improved by practicing thethermal treatment as described in said U. S. Patent No. 2,041,493, inthe presence of inorganic halides which are not volatile or but littleso at the temperatures employedfor the said thermal treatment. Also theproperties of other nickel-iron powders, for instance of a powderobtained by evaporating an aqueous solution containing the nitrates ofnickel and iron, glowing and reducing the residue and comminuting themass, can be considerably improved by annealing the obtained powder inthe presence of halides of the abovementioned nature. The same is truewith finely divided iron which has been prepared by comminuting ironpieces to powder form.

Water soluble inorganic halides, as for example sodium chloride, bariumchloride or other alkali metal or alkaline earth metal halides, are

very suitable for the said purpose, since they may be readily removedand recovered without losses from the powder after the thermaltreatment, by lixiviation with water. The metallic powder thus obtainedcan be worked into mass cores in known manner together with aninsulation material most suitable for the purpose. In some cases thelixiviation may be advantageously carried out by means of organicsolvents, such as alcohol, for example if the metallic powder is easilyoxidized by water. It is not necessary to completely remove the halides.by lixiviation; an unremoved portion of it acts as an insulation meansin the manufacture of the cores.

The amount of halides to be added to the powder may vary within widelimits, but should be in all cases so calculated as to prevent thepowder particles from sintering. It is preferable to use from 1 to 30parts by weight of a halide to 100 parts by weight of the metallicpowder.

The addition substances are preferably mixed as intimately as possiblewith the powder, for example by grinding them in a ball mill or makingthem into a paste by means of a solution or a suspension of the additionsubstance.

It offers no difliculty to incorporate the powder with further metalcomponents by adding to the mixture a readily reducible metal compound,for example a copper. or cobalt compound, as the chlorides of the saidmetals, and glowing the mass in a reducing atmosphere.

Th following examples will further illustrate how the present inventionmay be carried out in practice, but the invention is not restricted tothe said examples.

Example 1 A nickeliron powder containing per cent of nickel andpreparedby thermal decomposition of a mixture of nickel carbonyl and ironcarbonyl, was worked up into mass cores firstly without pretreatment(core No. l), secondly after a previously proposed treatment (core No.2) and thirdly after a treatment according to the present invention(core No. 3) A mixture of waterglass and kaolin was used in each case asthe insulation medium. The data of the electric and magnetic propertiesof these cores are the follow- In the pretreatment for core No. 2 thenickeliron powder was made into a paste with per cent of aluminiumhydroxide sol and heated at 1000 C. for 6 hours in a hydrogenatmosphere. The lumps formed were reduced to a fine powder by grindingin a ball mill for 24 hours, of which powder 80 per cent passed througha sieve with 10,000 meshes per square centimeter. The sifted portion washeated at 700 C. for 3 hours in a hydrogen current, again ground for 6hours and passed through a sieve with 10,000 meshes per square ntimeter.

According to the present invention (core No. 3) the nickel-iron powderwas finely ground with 30 per cent of its weight of sodium chloride in aball mill and heated at 1000 C. for 4 hours in a hydrogen current. After30 minutes grinding the product had already been reduced to sumcie'ntfineness. After dissolving out the sodium chloride by means of water thepowder was heated again at 800 C. for 5 hours in a hydrogen current,ground for a short time and passed through a sieve with 10,000 meshesper square centimeter.

Example 2 der so obtained was worked up into mass cores firstly withoutpretreatment (core No. 4),secondly after a previously proposed treatment(core No. 5) and thirdly after a treatment according to the presentinvention (core No. 6). A mixture of water-glass and kaolin was used ineach case as insulating medium. In the pretreatment for core N0. 5 thenickel-iron powder was made into a paste by means of 5 per cent ofaluminium hydroxide sol and glowed at 950 C. for 6 hours in a hydrogenatmosphere. The glowed mass was ground, again heated for 4 hours at 900C. in a hydrogen atmosphere and passed through a sieve with 16,900meshes per square centimeter.

According to the present invention (core No. 3) the nickel-iron powderwasmixed with 30 per cent of barium chloride, heated at 950 C. for 6hours in a hydrogen atmosphere and ground. After dissolving out thebarium chloride with water, the powder was again heated at 900 C. for 4hours in a hydrogen atmosphere and sifted through a sieve with 16,900meshes per square centimeter.

By comparison of the three cores the following data were found:

An iron powder obtained by grinding compact iron pieces is divided intotwo portions.

, Portion 1 is made into a paste with 5 per cent of aluminium hydroxidesol, heated at also? 0.

for 6 hours in a hydrogen atmosphere. groimd, again glowed at 800 C. for6 hours and passed through a sieve with 10,000 meshes per square meshesper square centimeter (core No. 8).

By comparison of both cores it was found that core No. '7 had apermeability of 63.1 and a hysteresis factor h Vin-45.9 whereas core No.8 had a permeability of 76.8 and a hysteresis factor What I claim is:

1. A process of producing pulverulent nickeliron alloys forelectromagnetic purposes which comprises thermally decomposing a mixtureof nickel carbonyl and iron carbonyl, coating the metal particles of theresulting powder with inorganic halides which are practically notvolatile at high temperatures and are selected from the class consistingof alkali metal and alkaline earth metal halides, heating the coatedpowder in a non-oxidizing atmosphere to a temperature of from about 500to about 1000 C. and removing the greater part of said halides from theheated particles.

2. The process as defined in claim 1 wherein said inorganic halide is analkali metal halide.

3. The process as defined in claim 1 wherein said inorganic halide is analkaline earth metal halide.

4. The process of producing pulverulent nickeliron alloys forelectromagnetic purposes which comprises thermally decomposing a.mixture of nickel carbonyl and iron carbonyl, coating the metalparticles of the resulting powder with sodium chloride, heating thecoated powder to 1000 C. in a current of hydrogen, grinding theresulting product, dissolving out the sodium chloride with water toremove the greater part thereof, and reheating the product to 800 C. ina current of hydrogen.

.. GEORG 'I'RAGESER.

